The invention relates generally to editing serially stored audio-visual information and in particular to a method and apparatus for playing back the serially stored material according to a selected sequence.
Copending applications U.S. Ser. No. 452,287 entitled "Video Composition Method and Apparatus", filed Dec. 22, 1982, now U.S. Pat. No. 4,538,188, and U.S. Ser. No. 556,539, entitled "Improved Video Composition Method and Apparatus", filed Dec. 2, 1983, disclose apparatus and methods for creating an edit decision list (EDL). The EDL identifies a continuous edited sequence of video and audio segments, drawn from unedited, raw source material, which together can define a complete program.
The preparation of the edit decision list requires many hours of work wherein the entire program or portions of the program are viewed repeatedly for technical and esthetic content. According to the above-identified applications, however, the editing process advantageously does not physically form new sequences of video segments each time an edit decision is made; but instead, the edit decisions are recorded in a digital memory, and the resulting selected scenes, defined by the EDL, are thereafter played back in the desired sequence. To accurately assess the effect of the sequence of segments, the sequences must be displayed, preferably in a contiguous fashion, from beginning to end, and should be capable of being repeatedly replayed.
One method of playing the sequence of segments according to the EDL is to create a master tape with the segments written thereon in the proper order. However, continuous rewriting of the master tape each time a new edit decision is made or each time a sequence is to be viewed, is to be avoided, and desirably another method should be provided for playing back the segments according to the EDL. When there are only a small number of segments to be played, for example three or four, each segment can be read from a different one (or two) of the many tape recorders which are available (according to the above-identified patent applications), and the segments can be played in sequence as the video tape recorders rewind to the beginning of a segment each time the segment has completed playing. If a video tape recorder does not have sufficient time to rewind and still play the segment when it is needed, two recorders can operate in serial sequence so that for small sequences of segments the problem is not severe and can be relatively easily handled.
On the other hand, when viewing an EDL having a long sequence of segments, for example when there are more segments than there are video tape recorders, it can result that absent proper organization, gaps develop in the playback of the segments which not only break concentration with respect to the portion of the sequence being viewed, but have the potential effect of disrupting the entire playback sequence. As noted above, it is not practical to record the segments, in accordance with the EDL, in a desired sequential order onto an output video tape recorder from the various source video tape recorders because that procedure is both time consuming and inflexible. If an editor changes the program after he has made the output tape recording, he must rerecord the entire program from the point of the change to the end of the program material. This is different, for example, than film editing, wherein shots or segments can be changed by simply pulling out an old shot and splicing a new one in its place.
It is therefore an object of the invention to provide reliable and flexible playback of audio-visual source material which enables a sequence of segments on an edit decision list to be played back in a generally contiguous, arbitrary order. Other objects of the invention are creating a contiguous display of selected segments of audio-visual source material and displaying a sequence of segments after modification of the sequence without rewriting the modified segments on a new tape and without physically cutting and rejoining them.